Many of currently widespread earphones are shaped to be put into the ears of a listener. For example, the inner ear type earphones have a shape to be hooked on the pinnae of the listener. In addition, the canal type earphones have a shape to be used by being put deeply into the ear holes (ear canals) (e.g., see Patent Document 1), often have a structure of hermetically sealed type, and have a relatively good sound insulation performance. Thus, there is an advantage that music can be enjoyed even in places with somewhat loud noise.
On the other hand, even when the listener wears the earphones and listens to the presented sound, the listener also needs to listen to ambient sound at the same time, for example, when the people around the listener speak to him/her. It is a dangerous situation if the listener cannot listen to the ambient sound. However, most of the conventional earphones such as the canal type are structured to close the ear holes almost completely in the wearing state. Thus, it is extremely difficult for the listener to listen to the ambient sound during listening and watching. Moreover, to the people around, the conventional earphones appear to close the ear holes of the listener in the wearing state. This gives the impression that it is hard to talk to the wearer of the earphones and inhibits communication between people.